In power plants, the flow control of fans is achieved by adjusting the opening of the baffles. This is an outdated method with poor economic efficiency and high energy consumption, resulting in rapid equipment damage, difficult maintenance, and high operating costs. A significant portion of the power is consumed during the baffle throttling process, leading to a huge waste of energy. [b]Renovation Scheme[/b] With the continuous development of electrical automation, high-voltage motor speed control products mainly include: electromagnetic speed control, hydraulic coupling speed control, pole changing speed control, ordinary single-stage speed control, internal feedback cascade speed control, and frequency conversion speed control. Frequency conversion speed control is a highly efficient speed control method that achieves speed control by changing the frequency of the motor stator. It has advantages such as high power factor, wide speed range, high speed accuracy, high speed efficiency, and rigid mechanical characteristics, and is an inevitable trend in the development of modern AC speed control. [b]Its characteristics are as follows:[/b] 1) Wide speed range: The speed range of high-voltage, high-capacity frequency converters can reach 0 to 100. 2) High adjustment precision and efficiency: within the normal speed range, the overall efficiency of the frequency converter is above 93%, and the power factor exceeds 0.95. 3) True soft start is achieved, with no impact on the motor and power grid. 4) Operation can be switched at any time in case of equipment failure, suitable for situations where downtime is not permissible. Changing the operating mode is easy; when the frequency converter fails, it can be switched to the mains frequency state via the bypass cabinet. However, currently, fan equipment cannot automatically switch to the mains frequency state when the frequency converter fails. Taking a induced draft fan as an example, when the fan is running at frequency, the fan damper is in the fully open position, and the fan speed is automatically adjusted according to the furnace negative pressure. When the frequency converter fails, technically, the bypass switch can be automatically activated, and the fan can run at the mains frequency. However, since the damper is in the fully open position, if it runs at the mains frequency, the suction volume will inevitably increase, easily causing boiler flameout. Therefore, the bypass switch automatic activation scheme in case of frequency converter failure still needs further research. In summary, high-voltage variable frequency speed control has gained a significant market share in recent years due to the following reasons: ① With the continuous improvement of high-voltage variable frequency technology, high-voltage variable frequency devices can now fully meet the requirements for safe and reliable operation in power plants. ② High-voltage variable frequency designs are becoming more rational, simple to use on-site, and easy to maintain. ③ Significant energy-saving effects and simple operation. ④ High power factor, which can avoid the impact of large currents during equipment startup. ⑤ With market competition, the price of high-voltage variable frequency drives has tended to decrease. ⑥ The harmonics of the variable frequency drive can also meet the requirements of the power grid. For these reasons, using high-voltage variable frequency drives is the preferred solution for the speed regulation retrofit of fan equipment in thermal power plants. The following is an explanation of the application of high-voltage variable frequency drives on the #3 boiler induced draft fan of the Xiahuayuan Power Plant for your reference. The system adopts a "one-to-one power frequency bypass scheme" retrofit, using a DCS control system as the regulation loop. **General Description of the Variable Frequency System:** Due to the high requirements of the ambient temperature for the variable frequency drive (VFD), generally below 40℃, a VFD room should be built for on-site installation. The normal operating power supply for the VFD is AC 220V, which can be drawn from the 380V section and the backup power section of the unit. Normally, one power supply is in operation while the other is on standby. If the AC power supply fails, the VFD can be powered by its UPS (1kVA) (the UPS can provide power for approximately 30 minutes). If the UPS power is insufficient, the backup DC 220V power supply will automatically activate. 10A DC fuses are added and installed in the high-voltage switchgear of each ventilator. The DC power failure monitoring signal and the VFD fault signal are connected in parallel to the VFD's comprehensive fault signal. When the DC power fails, a VFD fault signal is displayed on the CRT screen in the boiler control room. If the VFD alarms during normal operation of the ventilator VFD, operators should check the fault information on the VFD control cabinet's industrial computer display and whether the DC power supply fuse has blown. In addition, a cooler, air conditioner, and lighting power supply box are installed in the inverter room to meet the cooling and lighting needs. During normal operation, the inverter can automatically adjust the inverter speed in a closed loop through the furnace negative pressure. According to the thermal automatic conditions, it can also be manually adjusted in an open loop, and finally output a 4-20mA signal. The speed of the induced draft fan is set. In the inverter operation screen of the CRT screen, there are three soft buttons for start, stop, and reset, which control the start, stop output and fault reset of inverters A and B respectively. During normal operation, if a minor fault occurs in the inverter that does not affect the operation, only an alarm will be sounded and the high-voltage switch will not trip. If a major fault occurs, the high-voltage switch will trip and an alarm will be sounded at the same time. [b]Protection Function and Parameter Setting Instructions[/b] 1.6kV High Voltage Cabinet Tripping Conditions 1) Press the "Emergency Stop" button on the cabinet door. 2) Inverter trips immediately upon input transformer coil overheating due to a major fault (≥130℃); unit major fault (overvoltage, fiber optic fault); inverter overcurrent (≥150A rated output current); inverter overload (≥120A rated output current, after 1 minute); effective field input tripping. 2. Inverter alarm conditions (intermittent flashing of audible and visual alarms on the control cabinet): 1) Transformer temperature ≥120℃; 2) Power unit cabinet fan failure; 3) Cabinet door open; 4) Controller not ready (inverter power-on self-test process); 5) Unit module fault (overheating, undervoltage, drive fault, power supply fault, phase loss) bypass operation alarm; 6) High ambient temperature (≥40℃); 7) Industrial computer crashes; 8) DC control power supply disappears. 3. Inverter and motor protection settings: 1) Load protection: inverse time limit, 1.2.In (In is the motor rated current), 60s; 2) Instantaneous overcurrent protection: 1.5.In. 3) Over/under voltage protection: 6kV±10. 4) Overspeed protection: 110.Ne (Ne is the rated speed of the motor). 4. Inverter process parameter setting: 1) Acceleration time: 0～750r/min, 80s. 2) Deceleration time: Rated speed to minimum speed (approximately 240r/min) 240s. 3) Maintain original speed when speed setting is lost (DCS output power-off protection position). 5. High-voltage inverter inspection and maintenance points: 1) Regularly check the indoor temperature, ensuring it does not exceed 40℃. If the temperature is too high, take appropriate measures. 2) Keep the room clean and hygienic. 3) Regularly check the inverter for abnormal noises or odors, whether the cabinet is overheating, and whether there are any odors from the exhaust vents. 4) Regularly check the airflow at the power cabinet's air inlet using an A4 sheet of paper (the A4 paper should be firmly held by the filter; if there are any problems, troubleshoot them promptly, replace the filter, or check if the fan is faulty). During the first month of inverter operation, take advantage of a shutdown opportunity to de-energize the inverter and tighten all incoming and outgoing cables and connections between power units. Thereafter, tighten them regularly every 6 months (including control lines), and clean the cabinet interior with a vacuum cleaner. 6) Regularly record the inverter's operating status (voltage, current, speed, and power, etc.). If a trip occurs, record the fault details, identify the cause, and eliminate it before restoring power. 7) When testing motor insulation, de-energize the inverter and disconnect its input and output switches. Never test motor insulation while the inverter is running to prevent damage. 8) Strengthen the maintenance of the inverter's power supply, preventing simultaneous AC and DC power outages. Strengthen the maintenance of the inverter room's air conditioning to ensure the inverter's cooling does not exceed the recommended temperature. 9) There is an emergency stop button on the inverter control cabinet panel. Pressing it trips the high-voltage switch, stopping the induced draft fan; pulling it out puts it in the normal operating position. During normal operation, accidental contact by personnel must be strictly prevented. Conclusion Energy conservation and environmental protection in power plants are mainly reflected in the efficient and safe operation of the system and the effective regulation of flow. With the increasing demands for economic efficiency in the production process of thermal power plants, power plants must pursue energy conservation and consumption reduction to improve economic efficiency. Promoting high-voltage frequency converters has significant social and economic benefits in optimizing the operation of power plant fan systems.